# Bandpass 101

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#### loddie

I would like to learn how to model bandpass enclosures. Mostly what I have found online is geared to making a one note box for car audio. I am interested in designing a bandpass box to have as wide a frequency response as possible (hopefully three octaves: 200-1400). The enclosure will feed into a Unity Horn (I have come across Patrick Bateman's threads)

Please suggest books and websites where I can learn more about bandpass enclosures. Also, what does "sqrt" represent in this formula: Fm=sqrt(Fh X FL)? Is it square root?

What are the best programs for modeling bandpass enclosures (multiple ports, etc)?

Thanks!

#### Ron E

In order to make a 4th order bandpass box to cover that range, you would need to make a port or PR with a resonance of ~sqrt(200*1400)=~500Hz. Yes, sqrt=square root

Designing short ports for such high resonances is a little tricky, not something a standard program will do well at all, probably will need some cut and try. Good luck.

I'm trying to imagine (without any calcs) a driver that would work in such an enclosure. Maybe a small sealed back midrange?

#### sreten

Hi,

The real question is why ? what is the point of a BP at those frequencies ?

/sreten.

#### loddie

Thanks Ron. I was thinking most software would struggle with this type of bandpass application. I will probably have to resort to trial and error.

Sreten, this reason is the application, an automobile. The dash, window, and pillars will form the horn. Bandpass allows the driver to be remotely located, although limited to be port constraints

#### Ron E

I think the whole concept is flawed. Using the bandpass port as some sort of sound channeling system isn't likely to work well. If the ports are longer than ~1/4-1/2 wavelength at any in band frequency because otherwise there will be port resonances in or near the passband. If your planned ports are shorter than this, then why bother with bandpass at all?

#### loddie

To get back on topic, does anyone have suggestions for excellent books and/or websites to further one's education of bandpass enclosures?

Thanks!

#### Thawach

hi

I think about bandpass that the airflow pass the port slowly.
The transience is not well. But The SPL is high. The automobile
like it. I don't know why it is.

#### Ron E

loddie said:
To get back on topic, does anyone have suggestions for excellent books and/or websites to further one's education of bandpass enclosures?

What is your math tolerance?

If low:
You can look at http://www.diysubwoofers.org
You can get the Loudspeaker Design Cookbook, from which most of the information at diysubwoofers is taken.
If high (Engineer, physicist):
You can learn about acoustic equivalent circuits and modeling, then you can read Earl Geddes' and Laurie Fincham's articles in the JAES. You can learn to model them yourself... Don't forget to model the complex impedance of the port. Prraps once you've mastered that you can model the flare rate of your windshield, etc...

Or you could just build it.

#### loddie

Unfortunately my math tolerance is now low. I've read the diysubwoofers site and played with their spreadsheet. I will pick up the LSD Cookbook and just start building! I already picked up Geddes "Audio Transducers" book

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